Storage is the #1 reason camera systems fail. Undersized drives = gaps in footage when you need it most. This guide gives you the exact formula, a mental calculator, and drive recommendations so you buy once and record for years.
Quick Formula Daily GB = Cameras × Mbps × 108 (for H.265). Example: 8 cams × 4 Mbps × 108 = 3,456 GB/day = 3.4 TB/day.
The Storage Formula (Memorize This)
Core Equation
GB per Day = (Cameras × Bitrate_Mbps × 3600 × 24) / (8 × 1024)
= Cameras × Bitrate_Mbps × 10.547
Simplified (H.265): Cameras × Mbps × 108 = GB/day (within 3%)
Simplified (H.264): Cameras × Mbps × 216 = GB/day (H.264 ≈ 2× H.265)
Bitrate Reference Table (2026 Typical)
Pro Tip: Enable H.265 (HEVC) on every camera/NVR. It halves storage vs H.264. All 2020+ cameras support it. If your NVR doesn't, upgrade the NVR.
Quick Mental Calculator (No Spreadsheet Needed)
Method: "Cameras × Mbps × Days × 0.1 = TB"
Formula check: 8 cams × 4 Mbps × 30 days × 0.108 = 10.4 TB (matches table: 9.8 TB ≈ close enough)
What Changes the Numbers (Multipliers)
Drive Selection Guide (2026)
Surveillance-Rated Drives Only
Never use: Desktop drives (WD Blue, Seagate Barracuda), NAS drives (WD Red, Seagate IronWolf) — not rated for 24/7 sequential write. Surveillance drives have firmware optimized for constant write streams.
Capacity Sweet Spots (2026 Pricing)
Recommendation: 8 TB or 10 TB for most 4–8 bay NVRs. 12–14 TB for 8+ bay RAID 6.
Complete Sizing Worksheet
Step 1: List Your Cameras
Step 2: Calculate Daily GB
Total_Mbps × 108 = GB/day (H.265)
16 × 108 = 1,728 GB/day ≈ 1.7 TB/day
Step 3: Apply Retention & Motion Factor
Step 4: Add RAID Overhead
Step 5: Pick Drives
For this example (25.5 TB usable, RAID 6):
- Option A: 5× 10 TB SkyHawk = 50 TB raw → 30 TB usable ✓ ($900)
- Option B: 4× 12 TB SkyHawk = 48 TB raw → 28.8 TB usable ✓ ($1,000)
- Option C: 6× 8 TB SkyHawk = 48 TB raw → 28.8 TB usable ✓ ($960)
Bandwidth vs Storage (Don't Forget Upload)
If you back up to cloud (Wasabi/B2/R2):
Rule: Local storage = primary. Cloud = backup (events only = 5–10% of local).
NVR-Specific Notes
Quick Reference Card (Print This)
┌─────────────────────────────────────────────────────────────┐
│ CCTV STORAGE QUICK CALC │
├─────────────────────────────────────────────────────────────┤
│ DAILY GB = CAMERAS × MBPS × 108 (H.265) │
│ DAILY GB = CAMERAS × MBPS × 216 (H.264) │
├─────────────────────────────────────────────────────────────┤
│ 4K @ 15fps H.265 ≈ 4 Mbps │ 2K @ 15fps H.265 ≈ 3 Mbps │
│ 1080p @ 30fps H.265 ≈ 2 Mbps │ 1080p @ 30fps H.264 ≈ 5 Mbps│
├─────────────────────────────────────────────────────────────┤
│ TB FOR N DAYS = DAILY_GB × N / 1000 │
│ MOTION-ONLY ≈ ×0.3 (quiet) to ×0.75 (busy) │
│ RAID 1 = 50% │ RAID 5 = 75% (3-disk) │ RAID 6 = 60% │
├─────────────────────────────────────────────────────────────┤
│ DRIVES: WD Purple / Seagate SkyHawk (surveillance ONLY) │
│ 8TB/10TB = sweet spot │ RAID 6 for 4K/30+ days │
└─────────────────────────────────────────────────────────────┘
Related Guides
- Cloud Storage vs Local Storage for Security Cameras — Tiered retention, Wasabi/B2, encryption
- Best Small Business Security Camera Systems — NVR sizing, RAID, drive selection
- DIY Security Camera Installation: Complete Guide — Cable, mount, configure
- PoE Camera Cable Running: DIY Installation — Power budget for PoE switches
- Common Security Camera Problems & Fixes — Recording gaps, HDD failures
Last updated: July 2026. Prices and drive models change — verify current specs before purchasing. H.265/HEVC licensing is royalty-free for hardware encoding as of 2024.